Having sex should be pleasing, why can't I enjoy sex?

Multiple reasons. There are many possible reasons why sex may not be enjoyable. Most commonly psychological factors play a big role, as in feelings of anger or resentment towards the partner. There may be physical reasons as well, such as pain with intercourse. This can stem from a variety of causes as well. It's best to see your doctor to discuss your particular case after a thorough exam.
Sex should feel good. Sex should be enjoyable. If it's not pleasing, then something's not right. If this is only 2nd attempt, more likely you & your partner aren't ready since your partner should take his/her time to make sure you're lubricated enough so that sex is fun, not painful. Or perhaps guilt from your religious & cultural background is weighing on you. Ps don't forget to make him wear a condom to prevent stds.
Vaginal spasm. Although a woman can easily diagnose her vaginismus, medical evaluation is recommended .Diagnosing vaginismus is quite simple. It requires identifying an inability, or great difficulty, with one or more of the following : finger, tampon, applicator, intercourse or gyn examination.